1. Field
The following description relates to a beamforming scheme for microwave power transmission.
2. Description of Related Art
A beamforming scheme is used to improve data transfer efficiency in wireless communication. A channel gain estimation scheme for beamforming may be divided into two types. The first type is a time reversal scheme in which a transmitter measures a microwave signal transmitted by a receiver and either checks the location of the receiver using direction-of-arrival (DOA) estimation or measures a channel gain up to the receiver using channel reciprocity. The second type is a scheme in which a transmitter controls its microwave phase based on whether the amount of received power at a receiver has been increased or not. In summary, in a conventional scheme, a beam is steered by checking the location of a receiver based on information transmitted by the receiver.
The time reversal scheme requires a very complicated hardware structure. A phase detector for measuring the phase of a signal from a receiver is used for a plurality of antennas deployed in a transmitter. Furthermore, a circuit for sending a microwave signal is also used for the receiver. In order to send a microwave signal, active circuit elements, such as a phase-locked loop and a local oscillator including a power amplifier, are typically included. Accordingly, energy consumption at the receiver can be significantly increased. The scheme for performing beamforming depending on whether the amount of received power at the receiver has been increased or not has a disadvantage in that a beamforming speed is very slow if it is used solely.